Sources of coherent optical pulses, such as lasers, optical parametric oscillators and amplifiers, etc., configured to produce outputs having very high peak intensities are used in a number of research applications. Such sources are commonly used in applications that include multi-photon microscopy, materials testing, and nonlinear spectroscopy. Many of these applications require high peak intensities and pulsewidths in the sub-picosecond pulse duration regime.
Typically, these sources of coherent optical pulses are used in conjunction with an optical system comprised of one or more optical components, including, without limitation, lenses, mirrors, modulators, acousto-optical modulators, optical crystals, etalons, gratings, optical fibers, and the like. The coherent optical pulses may propagate through a variety of materials, including, without limitation, air, glass, optical coatings applied to one or more optical devices, and the like. The amount of time required for the light to propagate through various optical components often varies as a function of wavelength, this property of optical components is called dispersion. As a result, a chirp may be introduced in the pulsed optical signal propagating through these components, i.e. different wavelength components are shifted in time within the pulse. As such, the pulse duration of the optical pulse becomes longer. Dispersion of an optical component is positive when longer wavelength light travels faster through the optical component than shorter wavelength light. If an optical pulse passes through an optical component with positive dispersion, the pulse becomes positively chirped, i.e. longer wavelength components are ahead of shorter wavelength components within the pulse. In ultra short coherent optical pulse applications (e.g. sub-picosecond and femtosecond) the high peak intensity optical pulse may be substantially degraded during its propagation through the optical system. For example, the peak intensity may be drastically reduced as the pulsewidth increases. Higher order distortion of the pulses is also common.
In response thereto, commonly a dispersion compensator may be positioned within the optical system. Typically, the dispersion compensator is configured to produce a dispersion of an opposite sign to the dispersion of the optical system and, ideally, of the same absolute value. For example, if the optical components within the optical system have positive dispersion and therefore introduce positive chirp into the optical signal, the dispersion compensator is configured to have negative dispersion and introduce negative chirp into the optical signal, thereby negating the positive dispersion of the optical system. Therefore, the pulsewidth in the output of the optical system is short again. While this approach has proven somewhat successful in the past, a number of shortcomings have been identified. For example, dispersion of both the optical system and the dispersion compensator changes significantly with pulse wavelength and not in the same manner. As such, applications requiring wide wavelength ranges require extensive tuning processes to produce compressed pulses over the full wavelength range of the optical system. These tuning processes tend to be time-consuming manual endeavors. Further, these tuning processes may need to be repeated frequently.
In light of the foregoing, there is an ongoing need for a system and method for automatically compensating for the dispersion for coherent optical pulses over a broad range of wavelengths.